move the SoftBody work into its own library, BulletSoftBody (work in progress)

src/BulletSoftBody/Jamfile

@@ -0,0 +1,8 @@
+SubDir TOP src BulletSoftBody ;
+
+Description bulletsoftbody : "Bullet Softbody Dynamics" ;
+Library bulletsoftbody : 
+  [ Wildcard *.h *.cpp ]
+;
+
+LibDepends bulletsoftbody : bulletdynamics bulletcollision  ;